1. Field of the Invention
This invention relates to an improved catalyst for the ammoxidation of propane and isobutane to its corresponding .alpha.,.beta.-unsaturated mononitriles (acrylonitrile and methacrylonitrile). Another aspect of the present invention is directed to the process in which propane and isobutane are reacted along with ammonia and oxygen in the presence of the catalyst to produce acrylonitrile and methacrylonitrile. The catalyst of the present invention may be utilized in a single pass or recycle process.
Nitriles, such as acrylonitrile and methacrylonitrile, have been industrially produced as important intermediates in the preparation of fibers, synthetic resins, synthetic rubbers and the like. The commercially dominant method for their production requires the ammoxidation of propylene or isobutylene in the presence of ammonia and oxygen at a high temperature in the gas phase in the presence of an ammoxidation catalyst.
However, in view of the price differential between propane and propylene, or the price difference between isobutane and isobutene, recent attention has been drawn to the development of a method and catalyst for the production of acrylonitrile or methacrylonitrile by an ammoxidation reaction wherein the lower alkane such as propane or isobutane is used as a starting material and such lower alkane is catalytically reacted with ammonia and an oxygen-containing gas in the presence of an ammoxidation catalyst.
Earlier attempts to develop an efficient process for the ammoxidation of propane to acrylonitrile produced either insufficient yields or processes that necessitated adding halogen promoters to the feed. The latter procedure would require not only reactors made of special corrosion resistant materials, but also a quantitative recovery or separation and removal of the promoter. This added cost eliminated the advantages of the propane/propylene price differential.
Recent published patent publications such as EPO 0767164-A1 and patents such as U.S. Pat. Nos. 5,231,214, 5,472,925: 5,422,328: 5,049,692 and 5,008,427 have been directed to ammoxidation catalyst systems which are directed to solving the problems of previous attempts at propane ammoxidation using specific catalysts. In particular, U.S. Pat. No. 5,008,427 assigned to the assignee of the present invention is specifically directed to a vanadium-antimony promoted catalyst for propane ammoxidation wherein the catalyst is calcined at temperatures of 780.degree. C. or higher. The catalyst of the present invention and the ammoxidation procedure disclosed herein is directed to an improvement in process and catalyst disclosed in EPO 0767164-A1, the '214 and the '427 patents.